This invention concerns a steering wheel in which a coating layer made of a soft synthetic resin is applied to a resin insert and a ring core metal disposed to a boss portion.
As steering wheels mounted to vehicles such as automobiles, there have been used those in which a coating layer is formed by applying coating material made of a soft synthetic resin to a pad or ring portion so as to provide a feeling of high quality and soft touch.
In conventional steering wheels, a soft coating layer such as one made of a soft vinyl chloride resin, or foamed urethane resin is sometimes formed onto the outer circumference of a core metal. However, since the soft coating layer itself is soft, no favorable feeling can be obtained upon gripping the ring, causing a feeling of collapse or displacement relative to to the core metal at the inside. Accordingly, as a countermeasure for avoiding the displacement of the soft coating layer relative to the core metal, there have been used such means as adhesive bonding for securing both of them, use of a core metal form with a circumferential groove for providing an anti-rotation characteristic, or use of a core metal disposed with a hard coating layer and a continuous groove formed in the circumferential direction along the core metal between the core metal and the soft coating layer for providing the anti-rotation characteristic.
In the case of forming a hard resin such as a polypropylene resin and acetylcellose to the outer circumference of the core metal, since the hard coating layer itself is rigid, it causes neither a feeling of collapse nor of displacement relative to the core metal.
In recent years, higher quality has been demanded more and more for automobiles and it has been intended to cover as far as the boss cover below the pad portion with a soft synthetic resin. Further, in the case of using, for example, a PVC resin as the coating material made of a soft synthetic resin, peeling from the end portion is liable to occur between the resin insert and the coating material by merely laminating the material to the resin insert disposed to the boss portion, since the coating material is soft and, therefor, the provision of peeling-preventive means is required for them.
Then, the peeling-preventive measures are taken generally as indicated below.
That is, a through hole is disposed to the rising wall in perpendicular to the rising wall of the resin insert, the coating material is intruded to the portion at the inside of the rising wall corresponding to the through hole and caused to flow to the inside of the through hole, thereby connecting the coating layer at the outer circumferential surface with the coating layer at the inner side.
In the case of using adhesives between the core metal of the ring and the soft coating layer in the prior art described above, pre-treatment for the application of the adhesives such as degreasing of the core metal or the maintenance and the handling of the adhesives become troublesome because they increase the manufacturing cost for the steering wheel. Further, in the case of using a continuous circumferential groove formed into the core metal itself or the hard coating layer, there has been a problem that although no rotation (displacement) occurs between it and the soft coating layer formed onto the outer circumference thereof in the direction in perpendicular to the circumferential direction of the ring due to the groove formed continuously described above, the groove is of no use for preventing the soft coating layer from displacing relative to the circumferential direction of the ring portion.
While on the other hand, in the case of laminating the coating material to the resin insert disposed on the boss portion, since the rising wall of the resin insert is formed usually in parallel with the direction of opening and closing a die in view of the molding work and the design, a special mechanism such as a slide core has to be provided on the die itself for forming a through hole in perpendicular to the rising wall simultaneously with the injection molding of the resin insert, which increases the manufacturing cost for the die and leads to an increase in the production cost of the steering wheel.